The study concerns the purification of synthetic and industrial textile wastewater containing the most common dye, Reactive Black 5 (RB5), by electrocoagulation. The experiments were carried out under conditions of high salinity (35 g×dm^-3 NaCl) in a strongly alkaline environment (pH 11–12). These conditions are characteristics of dye-baths. The color and chemical oxygen demand (COD) removal were compared while the use of iron (steel) and aluminum (iron) electrodes. The biological oxygen demand (BOD₅) was tested as well. High efficiency of color removal, about 90%, was observed in a very short time: 3 and 10 minutes for iron and aluminum electrodes, respectively. The experiments showed that the effectiveness of color reduction depends on the material of the electrodes. However, there was no significant reduction in COD for both types of electrodes, which was related to the residual impurities in the liquid phase (by-products of RB5 and dissolved iron and aluminum compounds). At the same time, the BOD₅ increased 10 times after the purification, which indicates enhance in biodegradability of the wastewater. The main conclusion was that the electrocoagulation is a complex process, which is determined by the physical and chemical phenomena associated with the electrodes material as well as the environment of the reaction.

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